Don't know if that big relay is for headlights or not..
Regarding the 100W spotties on the wires dangling down.... Don't ! Never ever trust British wiring in a car. - IMHO it is marginal at best, so won't like a doubling of the load. Use the danglers to fire a relay which feeds the spotties.
Personally, I'd use a 50W 'Plus 50/90/100/whatever, as they may produce more light than a 'standard ' 100W globe.

